甲、乙两列电磁波的波长之比为1:3，则两列波的频率之比为 [ ]
A、1:3
B、3:1
C、1:1
D、无法判断
答案：B
西安事变发生后，中 * * 党派到西安调停的是[ ]
A、
B、
C、
D、
—Can you tell me _____?
—He is in the library. [ ]
A. where was Jack
B. where Jack was
C. where is Jack
D. where Jack is
